Merge pull request #398 from glimmerjs/fix-expand-signature

Fix ExpandSignature & ArgsFor

packages/@glimmer/component/addon/-private/component.ts

@@ -17,6 +17,7 @@ export function setDestroyed(component: GlimmerComponent<object>): void {
 interface ArgsSetMap extends WeakMap<Args<unknown>, boolean> {
   get<S>(key: Args<S>): boolean | undefined;
   set<S>(key: Args<S>, value: boolean): this;
+  has<S>(key: Args<S>): boolean;
 }
 
 // SAFETY: this only holds because we *only* acces this when `DEBUG` is `true`.
@@ -48,11 +49,13 @@ declare const Empty: unique symbol;
  */
 export type EmptyObject = { [Empty]?: true };
 
-type GetOrElse<Obj, K, Fallback> = K extends keyof Obj ? Obj[K] : Fallback;
+type GetOrElse<Obj, K extends PropertyKey, Fallback> = Obj extends { [Key in K]: infer U }
+  ? U
+  : Fallback;
 
 /** Given a signature `S`, get back the `Args` type. */
-type ArgsFor<S> = 'Args' extends keyof S
-  ? S['Args'] extends { Named?: object; Positional?: unknown[] } // Are they longhand already?
+type ArgsFor<S> = S extends { Args: infer Args }
+  ? Args extends { Named?: object; Positional?: unknown[] } // Are they longhand already?
     ? {
         Named: GetOrElse<S['Args'], 'Named', EmptyObject>;
         Positional: GetOrElse<S['Args'], 'Positional', []>;
@@ -65,11 +68,11 @@ type _ExpandSignature<T> = {
   Args: keyof T extends 'Args' | 'Element' | 'Blocks' // Is this a `Signature`?
     ? ArgsFor<T> // Then use `Signature` args
     : { Named: T; Positional: [] }; // Otherwise fall back to classic `Args`.
-  Blocks: 'Blocks' extends keyof T
+  Blocks: T extends { Blocks: infer Blocks }
     ? {
-        [Block in keyof T['Blocks']]: T['Blocks'][Block] extends unknown[]
-          ? { Params: { Positional: T['Blocks'][Block] } }
-          : T['Blocks'][Block];
+        [Block in keyof Blocks]: Blocks[Block] extends unknown[]
+          ? { Params: { Positional: Blocks[Block] } }
+          : Blocks[Block];
       }
     : EmptyObject;
 };
@@ -230,8 +233,8 @@ export default class GlimmerComponent<S = unknown> {
    * @param owner
    * @param args
    */
-  constructor(_owner: unknown, args: Args<S>) {
-    if (DEBUG && !ARGS_SET.has(args)) {
+  constructor(owner: unknown, args: Args<S>) {
+    if (DEBUG && !(owner !== null && typeof owner === 'object' && ARGS_SET.has(args))) {
       throw new Error(
         `You must pass both the owner and args to super() in your component: ${this.constructor.name}. You can pass them directly, or use ...arguments to pass all arguments through.`
       );